This application relates generally to predicting acoustic sound power and more particularly to predicting acoustic sound power from mechanical vibration in a disc drive.
Disc drive customers are demanding increasingly quieter disc drives. This is especially apparent with the advent of personal video devices that include disc drives and often reside in bedrooms, operating while people sleep. The standard measure of acoustic noise in disc drives is sound power (Lwa), which is measured in bels or decibels (dB). Lwa is independent of the measuring environment because it accounts for factors such as the distance of microphones from the sound source, atmospheric pressure, etc.
However, Lwa is extremely difficult to measure. Presently, Lwa measurements are performed in expensive anechoic chambers and require electronic equipment, such as spectrum analyzers, computers, microphones, and signal conditioners.
Attempts have been made to use mechanical vibration measurements to estimate Lwa. One such method involves measuring the vibration at one or more points on the disc drive and then summing the energy in the vibration as a time domain root mean square (RMS) signal. Other methods involve taking a fast Fourier transform of the mechanical vibration and summing all the peaks in the frequency domain. None of the prior methods produced an acceptable correlation between mechanical vibration and Lwa.
Accordingly there is a need for a method and testing system that uses mechanical vibration to accurately estimate Lwa. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
Against this backdrop the present invention has been developed. An embodiment of the present invention may be described as a method of estimating acoustic sound power produced by a disc drive. The method includes selecting a subset of predictive frequencies from a set of disc drive frequencies consisting essentially of operational driving frequencies in the disc drive and system resonance frequencies in the disc drive. Correlation constants are determined that correlate sound power to mechanical vibration magnitudes at each of the frequencies in the subset of predictive frequencies. The method further includes acquiring mechanical vibration data from the disc drive while operating the disc drive and determining predictive vibration magnitudes at each of the frequencies in the subset of predictive frequencies from the mechanical vibration data. Finally, the method includes determining an estimated acoustic sound power value for the disc drive from the determined correlation constants and the predictive vibration magnitudes.
An embodiment of the present invention may be alternatively described as a method of correlating mechanical vibration to acoustic sound power of disc drives using a representative is group of disc drives. The method includes selecting a subset of predictive frequencies from a set of disc drive frequencies consisting essentially of operational driving frequencies in the group of disc drives and system resonance frequencies in the group of disc drives. The method also includes acquiring mechanical vibration data while operating each disc drive in the group of disc drives, and determining predictive mechanical vibration magnitudes at each of the predictive frequencies for each disc drive in the group of disc drives. The method further includes determining an operating acoustic sound power value for each disc drive in the group of disc drives and determining a correlation between vibration magnitude at the predictive frequencies and sound power using the determined mechanical vibration magnitudes and the determined operating acoustic sound power values.
Another embodiment of the present invention may be described as a testing system for estimating sound power values in a subject disc drive. The system includes a transducer communicating with the subject disc drive and producing vibration data including vibration magnitudes of the subject disc drive at a subset of predictive frequencies selected from a set of disc drive frequencies consisting essentially of operational driving frequencies in the subject disc drive and system resonance frequencies in the subject disc drive. The system also includes means for determining an estimated acoustic sound power value for the subject disc drive from predetermined correlation constants and the vibration magnitudes.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.